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    The <strong>LLDB</strong> Debugger
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    	<div class="post">
    	  <h1 class="postheader">Adding Programming Language Support to LLDB</h1>
    	  <div class="postcontent">
    	    <p>
              LLDB has been architected to make it straightforward to
    	      add support for a programming language. Only a small
    	      enum in core LLDB needs to be modified to make LLDB
    	      aware of a new programming language. Everything else can
    	      be supplied in derived classes that need not even be
    	      present in the core LLDB repository. This makes it
    	      convenient for developers adding language support either
    	      in branches or downstream repositories since it
    	      practically eliminates the potential for merge
    	      conflicts.
            </p>
            <p>
              The basic steps needed are as follows:
              <ul>
                <li>Add the language to the LanguageType enum</li>
                <li>Add a TypeSystem for the language</li>
                <li>Add expression evaluation support</li>
              </ul>
            </p>
            <p>
              Additionally, you may want to create a Language and LanguageRuntime plugin for your language, which enables support for advanced features like dynamic typing and data formatting.
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    	<div class="post">
    	  <h1 class="postheader">Add the Language to the LanguageType enum</h1>
    	  <div class="postcontent">
            <p>
              The LanguageType enum
              (see <a href="http://llvm.org/svn/llvm-project/lldb/trunk/include/lldb/lldb-enumerations.h">lldb-enumerations.h</a>)
              contains a list of every language known to LLDB. It is
              the one place where support for a language must live
              that will need to merge cleanly with core LLDB if you
              are developing your language support in a separate
              branch. When adding support for a language previously
              unknown to LLDB, start by adding an enumeration entry to
              LanguageType.
            </p>
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    	  <h1 class="postheader">Add a TypeSystem for the Language</h1>
    	  <div class="postcontent">
            <p>
              Both <a href="http://llvm.org/svn/llvm-project/lldb/trunk/include/lldb/Core/Module.h">Module</a>
              and <a href="http://llvm.org/svn/llvm-project/lldb/trunk/include/lldb/Target/Target.h">Target</a>
              support the retrieval of a TypeSystem instance via
              GetTypeSystemForLanguage(). For Module, this method is
              directly on the Module instance. For Target, this is
              retrieved indirectly via the TypeSystemMap for the
              Target instance.
            </p>
            <p>
              The TypeSystem instance returned by the Target is
              expected to be capable of evaluating expressions, while
              the TypeSystem instance returned by the Module is not.
              If you will support expression evaluation for your
              language, you could consider following one of these
              approaches:
              <ul>
                <li>
                  implement a single TypeSystem class that supports
                  evaluation when given an optional Target,
                  implementing all the expression evaluation methods
                  on the TypeSystem in this case, OR
                </li>
                <li>
                  create multiple TypeSystem classes, one for
                  evaluation and one for static Module usage.
                </li>
              </ul>

              For clang and Swift, we chose to go with the latter,
              primarily to make it clearer that evaluation with the
              static Module-returned TypeSystem instances make no
              sense, and have them error out on those calls. But
              either approach is fine to pursue.
            </p>
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    	  <h1 class="postheader">Add Expression Evaluation Support</h1>
    	  <div class="postcontent">
            <p>
              Expression Evaluation support is enabled by implementing
              the relevant methods on a TypeSystem-derived class.
              Search for "Expression" in the
              <a href="http://llvm.org/svn/llvm-project/lldb/trunk/include/lldb/Symbol/TypeSystem.h">TypeSystem header</a>
              to find relevant
              methods to implement.
            </p>
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    	  <h1 class="postheader">Type Completion</h1>
    	  <div class="postcontent">
            <p>
              There are three levels of type completion, each
              requiring more type information:
              <ol>
                <li>
                  Pointer size: when you have a forward decl or a
                  reference, and that's all you need.  At this stage,
                  the pointer size is all you need.
                </li>
                <li>
                  Layout info: you need the size of an instance of the
                  type, but you still don't need to know all the guts
                  of the type.
                </li>
                <li>
                  Full type info. Here you need everything, because
                  you're playing with internals of it, such as
                  modifying a member variable.
                </li>
              </ol>
              Ensure you never complete more of a type than is needed
              for a given situation. This will keep your type system
              from doing more work than necessary.
            </p>
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    	  <h1 class="postheader">Creating Types</h1>
    	  <div class="postcontent">
            <p>
              Your TypeSystem will need an approach for creating types
              based on a set of Modules.  If your type info is going
              to come from DWARF info, you will want to subclass
              <a href="http://llvm.org/svn/llvm-project/lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFASTParser.h">DWARFASTParser</a>.
            </p>
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    	  <h1 class="postheader">Language and LanguageRuntime plugins</h1>
    	  <div class="postcontent">
            <p>
              If you followed the steps outlined above, you already have taught LLDB a great deal about your language. And if your language's runtime model and fundamental data types don't differ much from the C model, you are pretty much done.
              <br/>
              However, it is likely that your language offers its own data types for things like strings, arrays, ..., and probably has a notion of dynamic types, where the effective type of a variable can only be known at runtime.
            </p>
            <p>
              These tasks are covered by two plugins:
              <ul>
                <li>a LanguageRuntime plugin, which provides LLDB with a dynamic view of your language; this plugin answers questions that require a live process to acquire information (e.g. dynamic type resolution)</li>
                <li>a Language plugin, which provides LLDB with a static view of your language; questions that are statically knoawble and do not require a process are answered by this plugin (e.g. data formatters)</li>
              </ul>
            </p>
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